1. Field of the Invention
The invention relates to a binding for winding overhangs of rotors of electric machines in accordance with the preamble of the first claim. It likewise relates to a method of producing a binding in accordance with the preamble of the independent method claim.
2. Discussion of Background
Such bindings for winding overhangs of rotors of electric machines are known from "Herstellung der Wicklung elektrischer Maschinen" [Production of the winding of electric machines], edited by H. Sequent, Springer Verlag, page 236 f. There, the windings of winding overhangs of the rotors of electric machines are retained by bindings made of steel wire or glass fibers impregnated with resin. A further mounting and supporting of winding overhangs, not described in that document, are cap rings. The wire bindings are formed from as far as possible only one layer of wire turns lying closely adjacent to one another. An insulating layer is placed between binding and winding. Bronze or nonmagnetic steel is used as winding wire material.
The thermosetting glass fiber bindings are composed of glass fiber tapes preimpregnated with resin, which are wound in multiple layers around the winding overhang. Advantages in terms of construction and production result from the use of thermosetting glass bindings. On the market, the widest possible range of glass fiber tapes with a thermosetting matrix can be obtained, for example glass fibers which are impregnated with a solvent-free resin. During the binding, operations are carried out with a pretension which is as high as possible, the maximum applicable pretension being dependent on the tensile strength of the glass fiber tape. The thermosetting binding material is heated so intensively by a heat source that the resin becomes liquid. As a result of the pretension, outer layers already penetrate into the lower layers during the binding, which results in a certain proportion of the pretension being lost before the resin has hardened. The pretension must be applied during the processing in such a way that the pretension remaining in the hardened material is sufficient to compensate for the centrifugal forces in the winding overhangs during operation. The advantages of glass bindings over wire bindings are, inter alia, the reduction in cost of the final product, special insulating layers are dispensed with, the specific elasticity is higher, lower loading by the centrifugal force as a result of lower weight, and so on.
However, the thickness of the binding needed is decisive as the selection criterion for the application of glass bindings or steel bindings for winding overhangs. Starting at a thickness of the thermosetting glass binding of over 8 mm, further turns of thermosetting fibrous material which are applied no longer have any effect on the strength of the glass binding. Therefore, when greater strength is needed, the glass bindings are replaced by steel bindings.